/**
 * A simple example program to use DataMonitor to start and
 * stop executables based on a znode. The program watches the
 * specified znode and saves the data that corresponds to the
 * znode in the filesystem. It also starts the specified program
 * with the specified arguments when the znode exists and kills
 * the program if the znode goes away.
 */
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

import org.apache.zookeeper.KeeperException;
import org.apache.zookeeper.WatchedEvent;
import org.apache.zookeeper.Watcher;
import org.apache.zookeeper.ZooKeeper;

public class Executor
    implements Watcher, Runnable, DataMonitor.DataMonitorListener
{
    String znode;

    DataMonitor dm;

    ZooKeeper zk;

    String filename;

    String exec[];

    Process child;

    public Executor(String hostPort, String znode, String filename, String exec[]) throws KeeperException, IOException 
    {
        this.filename = filename;
        this.exec = exec;
        zk = new ZooKeeper(hostPort, 3000, this);
        dm = new DataMonitor(zk, znode, null, this);
    }

    /**
     * @param args
     */
    public static void main(String[] args) 
    {
        if (args.length < 4) 
        {
            System.err
                    .println("USAGE: Executor hostPort znode filename program [args ...]");
            System.exit(2);
        }
        String hostPort = args[0];
        String znode = args[1];
        String filename = args[2];
        String exec[] = new String[args.length - 3];
        System.arraycopy(args, 3, exec, 0, exec.length);
        try 
        {
            new Executor(hostPort, znode, filename, exec).run();
        } 
        catch (Exception e) 
        {
            e.printStackTrace();
        }
    }

    /***************************************************************************
     * We do process any events ourselves, we just need to forward them on.
     *
     * @see org.apache.zookeeper.Watcher#process(org.apache.zookeeper.proto.WatcherEvent)
     */
    public void process(WatchedEvent event) 
    {
        dm.process(event);
    }

    public void run() 
    {
        try 
        {
            synchronized (this) 
            {
                while (!dm.dead) 
                {
                    wait();
                }
            }
        } 
        catch (InterruptedException e)
        {
        }
    }

    public void closing(int rc) 
    {
        synchronized (this)
        {
            notifyAll();
        }
    }

    static class StreamWriter extends Thread
    {
        OutputStream os;

        InputStream is;

        StreamWriter(InputStream is, OutputStream os)
        {
            this.is = is;
            this.os = os;
            start();
        }

        public void run() 
        {
            byte b[] = new byte[80];
            int rc;
            try 
            {
                while ((rc = is.read(b)) > 0) 
                {
                    os.write(b, 0, rc);
                }
            } 
            catch (IOException e) 
            {
            }

        }
    }

    public void exists(byte[] data) 
    {
        if (data == null) 
        {
            if (child != null) 
            {
                System.out.println("Killing process");
                child.destroy();
                try 
                {
                    child.waitFor();
                } 
                catch (InterruptedException e) 
                {
                }
            }
            child = null;
        } 
        else 
        {
            if (child != null) 
            {
                System.out.println("Stopping child");
                child.destroy();
                try 
                {
                    child.waitFor();
                } 
                catch (InterruptedException e) 
                {
                    e.printStackTrace();
                }
            }
            try 
            {
                FileOutputStream fos = new FileOutputStream(filename);
                fos.write(data);
                fos.close();
            } 
            catch (IOException e) 
            {
                e.printStackTrace();
            }
            try
            {
                System.out.println("Starting child");
                child = Runtime.getRuntime().exec(exec);
                new StreamWriter(child.getInputStream(), System.out);
                new StreamWriter(child.getErrorStream(), System.err);
            } 
            catch (IOException e) 
            {
                e.printStackTrace();
            }
        }
    }
}